The invention relates to a method of producing accurately scaled, well-defined surfaces of workpieces from carbonaceous cast iron and having tribologic properties, more particularly of cylinders of internal combustion engines.
A method for producing the working surfaces of cylinders of internal combustion engines is described in West German Patent Application P 31 19 847.3-14. In this method, the working surface of the cylinder is subjected to various operating cycles consisting of an electrochemical removal and a mechanical friction-cladding removal, so that a dimensionally accurate, tribologically suitable surface can be achieved. During the mechanical removal of the electrolytically treated surface, the protruding graphite is removed without causing the open graphite flakes and resulting pockets to be smeared shut by adjacent metallic material. Moreover, surface constituents of the base material, particularly mixed crystals, are abraded and subsequently clad by rolling. This results in a surface in which bearing, flat plateaus which are partially clad with graphite, mixed crystals and/or possible electrolytic residues, alternate with open graphite flakes. Compared with previous bright surfaces, such a surface has a dark-glossy appearance.
When mass-producing such surfaces, it has proved to be problematical to make well-defined surface structures that can be reproduced as required. This is because, among other things, work materials of the workpieces to be machined differ, due to tolerances, in their chemical composition and mechanical properties, as well as to tolerances during the prefinishing.
The object of the invention is to provide a method that is particularly suitable for mass production and which ensures the production of well-defined, tribologically suitable, dimensionally accurate surfaces of constant quality.
This object is achieved in accordance with the invention with the characterizing features of claim 1. As discovered by the inventors, "by fixing a specified ratio between the electrochemical and mechanical surface removals of the last operating cycle and by including this in the total removal ratio, a constant, well-defined surface quality can be achieved."
Features of the invention result in a very favorable surface which is more particularly suited for working surfaces of cylinders of internal combustion engines with respect to the running-in and wear characteristics. A first operating cycle can already occur with constant predetermined data for the electrochemcial and mechanical stock removal, advantageous conclusions can be drawn that are essential with respect to the other operating cycles and the definitive surface quality desired. In this way, a process control can be provided which contributes significantly toward achieving a surface quality that can be produced within the shortest production time possible.
Process steps are carried out continuously during fabrication, preferably by means of a processor. The processor determines, in accordance with the actual dimensions of the workpiece, the total stock removal ratio, the particular ratio between theoretical and actual stock removal, and computes the required intermediate operating cycles, taking account of the last stock removal ratio computed.